In acute experiments with 20 isolated cat hearts, corinfar (0.1, 1, and 10 micrograms) and nitroglycerin (1, 10, and 100 micrograms) and their combination were tested for their effects on cardiac vessels and performance. Corinfar and nitroglycerin were found to exert a dose-dependent coronary dilating effect; however, more pronounced and prolonged action was shown by corinfar. The combination of the drugs produced more rapid and prolonged decrease in coronary artery tone when they were given alone. Nitroglycerin failed to affect venous return from the coronary bed and cardiac function, whereas corinfar increased venous return in most cases and decreased it in some cases, exhibited negative ino- and chronotropic effects, and reduced myocardial oxygen consumption.